Recently, manufacturing processes of Thin Film Transistor (TFT) array substrate and LTPS needs to ensure that there is no misalignment between multilayered stack structures. Therefore, in the processes of stacking the multilayered structures, it is needed to monitor and measure misalignment between layers and to adjust the misalignment in time. If there is an error in the misalignment measurement, it may influence subsequent processes, resulting in a decline in product yield. Generally, a box type mark is adopted as a basis for judging an alignment in order to improve accuracy of misalignment measurement and thereby to meet requirements of high resolution. As shown in FIG. 1, the n-th stacked layer (for example the first layer) is taken as a reference layer 100, and the (n+m)-th layer (for example the second layer) is taken as an alignment layer 200. A frame shaped reference mark A is arranged around the reference layer 100, and a square alignment mark B is arranged in the middle of the alignment layer 200. If the center of the reference mark A is aligned with the center of the alignment mark B, that is, the alignment mark B is located in the middle position of the frame shaped reference mark A, there is no misalignment between the n-th layer and the (n+m)-th layer. If the center of the reference mark A does not overlap with the center of the alignment mark B, there is a misalignment between the n-th layer and the (n+m)-th layer. The misalignment is measured using inspection and measuring equipments, namely, the misalignment obtained by deducting the center of line L2 from the center of line L1 in FIG. 1 is measured.
Another type of existing reference layer 100 is shown in FIG. 2. Four edges around the reference layer are not joined together, but measurement principle is the same as FIG. 1.
The conventional technologies as described above have shortcomings as follows:
Misalignments can only be judged using inspection and measuring equipments. Pattern defects or faults in the inspection and measuring equipments may cause that misalignments are not accordant to actual situation, and feedback of the wrong misalignments to an exposure machine may result in an exposure data error.
Hence, in the conventional technologies, misalignments are judged only depending on inspection and measuring equipments, it is difficult to measure these slight misalignments using other measuring equipments, thereby resulting in difficulties in judgment of measurement accuracy and thereby high error rate.
The above information disclosed in the background portion is only for the purposes of enhancing understanding of the background of the present disclosure, and thus it may include information which does not constitute prior art known to one of ordinary skill in this art.